Support surfaces such as mattresses and seat cushions that include air chambers have application for supporting people who are bed-ridden, confined to a chair or the like. A wide range of air mattresses and air cushions are suggested in the patent literature. Some such air mattresses and air cushions include controllers that control the operation of pumps and/or valves to inflate or deflate the air chambers and thereby automatically provide a required degree of support while reducing pressure points and the like.
In general it is desirable to minimize the interface pressure between the person and support surface. By doing so one can improve the health and comfort of the occupant. However, if the air pressure is too low then the person may “bottom out”. This is undesirable as bottoming out can be uncomfortable for the occupant and can even negate the benefit that the support surface is intended to provide.
Patents in the field of cushions or mattresses that include inflatable chambers include: U.S. Pat. No. 4,799,276; U.S. Pat. No. 6,721,980; U.S. Pat. No. 4,949,412; and U.S. Pat. No. 5,283,735. U.S. Pat. No. 4,554,930; U.S. Pat. No. 6,030,351 and U.S. Pat. No. 5,253,656 show pressure sensors for use on a bed or the like. U.S. Pat. No. 6,058,537 shows an air mattress with sensors for determining the location of a person. U.S. Pat. No. 5,237,501; U.S. Pat. No. 6,034,526; U.S. Pat. No. 5,539,942; U.S. Pat. No. 4,542,547 and U.S. Pat. No. 6,870,341 disclose related technologies. Other patient supports are disclosed in U.S. Pat. No. 5,630,238 U.S. Pat. No. 5,715,548; U.S. Pat. No. 6,076,208; U.S. Pat. No. 6,240,584; U.S. Pat. No. 6,320,510; U.S. Pat. No. 6,378,152; and U.S. Pat. No. 6,499,167.
Some existing systems have controllers that control the air pressure in the air chambers. In some cases, such controllers determine the pressure of air to maintain in the air chambers based upon the weight of the occupant. Existing systems may require an attendant to enter the desired air pressure, or to enter the occupant's weight. Other existing systems automatically determine the air pressure based on feedback from weight sensors which measure the weight of the occupant.
Such existing systems have several shortcomings. One shortcoming is that the air pressure is determined largely on the basis of the occupant's weight. However, different persons of similar weight may have vastly different body shapes. Consider, for example, a 200 lb, 6′-3″ tall man versus a 200 lb, 4′-11″ tall woman. Although in reality the air pressure that minimizes the interface pressure between the support surface and the occupant is different for each occupant, existing systems cannot automatically accommodate such differences because the necessary sensory inputs are not available.
Another shortcoming of the existing systems is that user interaction is required to set up the air pressure. For example, a user (typically a nurse) may enter the occupant's weight. Alternatively, the user may be required to “tare” the system while the support surface is unoccupied, in order for it to subsequently determine the occupant's weight with the required accuracy.
Other existing systems control the air pressure based on the measurement of the interface pressure between the support surface and the occupant (see for examples U.S. Pat. No. 4,799,276; U.S. Pat. No. 6,721,980, and U.S. Pat. No. 5,283,735). In these systems, the air pressure may be regulated so that the interface pressure between the occupant and the support surface does not exceed a predetermined threshold. In general these systems suffer from the shortcoming that the presence of the sensors required to measure the interface pressure itself causes detrimental interface pressures.
There remains a need for support surfaces that alleviate or overcome these shortcomings.